A holographic optical element having a volume hologram recording layer functions as a light combiner and is applied to an optical lens, a display element, or the like, and thus there is increasing demand for it. In particular, a holographic optical element as a display element of head-mounted display or head-up display has high transparency of a volume hologram recording layer, and thus it can be used as a display element of a see-through type (for example, JP 2014-215410 A).
Being accompanied with the increasing demand or diversified uses, the holographic optical element is required to have higher performance and quality items are becoming more diversified. For a display element of see-through type, high diffraction efficiency of a volume hologram recording layer is required to display information light in the presence of external light (background). Furthermore, in order to display information with good accuracy, it is required to avoid an occurrence of a ghost by suppressing unnecessary light reflection within a display element.
Production of a volume hologram recording layer is generally achieved by face-to-face exposure (interference exposure) of a photosensitive layer which is sandwiched between a pair of transparent supports and obtained by coating and drying of a photosensitive composition containing polymerizable monomer with coherent light source, and forming a diffraction grating consisting of areas with high refractive index and low refractive index by allowing an occurrence of polymerization reaction in the photosensitive layer according to interference wave (for example, JP 6-301322 A).